Presto equivalent of MySQL group_concat

问题

I'm new to Presto and looking to get the same functionality as the group_concat function in MySQL. Are the following two equivalent? If not, any suggestions for how I can recreate the group_concat functionality in Presto?

MySQL:

select 
  a,
  group_concat(b separator ',')
from table
group by a

Presto:

select 
  a,
  array_join(array_agg(b), ',')
from table
group by a

(Found this as a suggested Presto workaround here when searching group_concat functionality.)

回答1:

Try using this in place of group_concat in Presto ::

select 
  a,
  array_join(array_agg(b), ',')
from table
group by a

回答2:

Also, if you're looking for unique values only – an equivalent to group_concat(distinct ... separator ', ') – try this:

array_join(array_distinct(array_agg(...)), ', ')

回答3:

There's no function as of this answer, though the feature has been requested.

The closest equivalent is mentioned in your question.

WITH tmp AS (
SELECT 'hey' AS str1
UNION ALL
SELECT ' there'
)
SELECT array_join(array_agg(str1), ',', '') AS joined
FROM tmp

来源：https://stackoverflow.com/questions/44142356/presto-equivalent-of-mysql-group-concat